(a) Field of the Invention
The present invention relates to linear roller guideway technology, and more particularly to a method and structure for improving the dynamic characteristics of a linear roller guideway for use in a precision machine tool, robotic or industrial automation equipment to provide a linear motion of low frictional resistance and to bear a load.
(b) Description of the Prior Art
Linear roller guideway is a high precision motion mechanism assembly, as illustrated in FIG. 1, generally comprising a rail 10, at least one slide unit (slider, slide block, or carriage) 20, and rolling elements 30. The slide unit 20 is adapted for holding and carrying work platforms and workpieces. The rolling elements 30 can be balls or rollers. By means of the rolling elements 30, the rail 10 and the slide unit 20 are movable relative to each other to further carry the work platform, achieving a high precision linear motion. Because the contact between the rail 10 and the slide unit 20 is points or a line, the frictional resistance is very low, about 2% of sliding friction, and the coefficient of friction is about 0.004.
According to the theory of elasticity, when an external force is applied to the surface of the slide unit 20, the rolling elements 30 in the linear roller guideway are slightly elastically deformed (see the imaginary line in FIG. 2). This elastic deformation is not a permanent deformation. After the external force disappears, the rolling elements 30 immediately return to their former shape. Thus, if the applied external force varies with time, or the size of the applied external force (e.g. the machine tool cutting force) is changed, a number of negative factors can arise during the elastic deformation process of the rolling elements 30. Therefore, many different design methods or techniques are developed. Throughout these methods or patents, in addition to the method of enabling a controller to actively make compensation, they can be roughly divided into several categories as follows:
(A) Increase the stiffness of the linear roller guideway by: reducing the elastic deformation of rolling elements, for example, changing the geometric size, amount and/or relative allocation of the rolling elements, or pre-stressing the rolling elements.
(B) Increase the damping force of the linear roller guideway by: enabling the elastic deformation of the rolling elements to be rapidly stopped, i.e., rapidly attenuating or stopping the vibration when it is produced, for example, putting a large amount of mini sliding components in between the slide unit and the rail, using high damping materials, or using a hydraulic slide unit having an oil film to provide a high level of damping properties.
(C) Improve the stiffness and damping of the linear roller guideway by: adding an additional nonlinear element. This method is a more progressive way in line with the industry's needs.